Hmm ... came across exactly the same issue using build 2.1 (922) (using F9 hide to tray) - ... 'hide inactive icons' was already disabled.
I fixed it by ENABLING 'hide inactive icons' and then immediately disabling it again.
I fully accept its probably an MS issue but since it cannot be said that 'disabling' that tray feature prevents the problem perhaps it might be worth adding a little note in the FAQs about how to fix it?
Just IMO ..
Cheers